Metal cast cooking unit having a temperature sensitive control sensor

ABSTRACT

A cooking unit of cast metal having a temperature sensitive control sensor cast therein including a temperature sensitive resistance element constructed and arranged in a casing or sheath so that it is capable of being cast directly into the metal mass, wherein the elements of the sensor will withstand the high temperatures in the casting processes and maintain its integrity.

United States Patent Finney [451 Oct. 31, 1972 [S4] METAL CAST COOKINGUNIT HAVING A TEMPERATURE SENSITIVE CONTROL SENSOR [72] Inventor: PhilipF. Finney, Villa Park, Ill.

v [73] Assignee: Thermo-Couple Products Company,

I Winfield, Ill. 22 Filed: July 16,1971

[21] Appl.No.: 163,318

Related US. Application Data [62] Division of Ser. No. 878,832, Nov. 21,1969,

Pat. No. 3,650,024.

[52] U.S.Cl. .Q ..219/449,99/331,219/494, 338/22R 51 Int. Cl. ..H05b3/68 [58] Field of Search.....'.219/200, 435', 436, 439, 441,

[56] References Cited UNITED STATES PATENTS 2,971,077 2/1961 Palmer..2l9/436 3,286,077 11/1966 Radford et al. ..2l9/494 X 3,383,493 5/1968Gellert ..2l9/544 X Primary Examiner-C. L. Albritton Attorney-James B.Kinzer et a1.

[57] ABSTRACT A cooking unit of cast metal having a temperaturesensitive control sensor cast therein including a temperature sensitiveresistance element constructed and arranged in a casing or sheath sothat it is capable of being cast directly into the metal mass, whereinthe elements of the sensor will withstand the high temperatures in thecasting processes and maintain its integrity.

8 Claims, 13 Drawing Figures P'ATE'N'TEDnm 31 m2 SHEET 1 BF 3 FIGJINVENTOR PHILIP F. FINNEY FIGS BY v v PATENTED mm 3 1 lsiz SHEET 2 OF 3SENSOR CURRENT SENSITIVE TING CONTROLLER UNIT FIG] INVEVNTOR PHILIP FFINNEY BY 7 7 AT ORNEYS METAL CAST COOKING UNIT HAVING A TEMPERATURESENSITIVE CONTROL SENSOR This application is a division of my copendingappli-.

cation, Ser. No. 878,832, filed Nov. 21, 1969, now U.S. Pat. No.3,650,024.

This invention relates in general to a cast metal cooking un'it having atemperature sensitive control sensor cast therein for determining andcontrolling 'the temperature of the cooking surface, wherein the sensorincludes a temperature sensitive resistance element the current orvoltage passing therethrough being proportionate to the temperature ofthe element, and wherein the sensor is capable of withstanding extremelyhigh temperatures present in metal casting processes thereby enabling itto be cast directly into a metal castmg. l

I-Ieretofore, conventional thermostats have been employed to control thetemperature of cooking surfaces of cooking units, and it is known thatthese thermostats do not pro'v'ideaccurate temperature control desiredto preserve flavor-and quality of food and to produce high rates ofefficiency. The demand for more accurate control than can be provided-byconventional thermostats has brought about the conception of the,present invention. r

Thesensor of the present invention satisfies the demands of the foodindustry in providing the necessary close temperature control of acooking surface in a cooking unit to maintain high eff ciency while atthesame time preserving flavor and quality of food. The sensor includesa uniquely constructed temperature sensitive resistance element incombination with. suitable terminals having a low coefficient ofresistance change with temperature change wherein the sensor may be castdirectly into a metal cooking unit'while maintainingits integrity duringthe casting process and providing suitable terminals from the cast massto thereafter be connected into control circuitry. Itwill be appreciatedthat the cooking unit may be heated by any suitable means such as a fuelburner or an electric'resistance heating element.

The sensor is connected into a control circuit so that it-forms a partof a voltage divider circuit or a wheatstone bridge. Vhere the sensormay be connected in a voltage divider circuit, a change in resistance inthe sensor will produce a proportionate change in voltage or current inthe circuit that will affect the pedestal voltage of a unijunctiontransistor in a solid state control which in turn operates the fuelburner or electric heating element. Where the sensor is connected in awheatstone bridge a change in sensor resistance due to a temperaturechange will affect the voltage or current in the wheatstone bridge tocause an unbalanced condition, wherein the resultant potential change isamplified to control a device that causes the energy input to the massto increase or decrease to counteract the energy loss or gain detectedby the sensor.

It is therefore an object of the present invention to provide animproved metal cast cooking unit having a temperature sensitive controlsensor cast therein.

Still another object of this invention is in the provision of a cookingunit having a sensor sensitive to temperature, and capable ofwithstanding handling under foundry conditions and therefore beingsufficiently rugged to allow placement and securing into metal moldingequipment, and wherein the sensor includes a temperature sensitiveresistance element protected against poured metal from contacting sameduring the casting process.

A further object of the invention is to provide a cooking unit includinga sensor having a metal sheath and refractory insulation to maintain thetemperaturev sensitive elementelectrically insulated from the sheath,and means for avoiding stresses on the temperature sensitive elementduring fabrication of the sensor.

Another object of the invention is in the provision of a temperaturesensitive control sensor capable of maintaining its integrity when castinto a metal mass, and.

-- cooking unit having-a sensor which includes a temperature sensitiveresistor assembly having a temperature sensitive wire wound on a ceramiccore and connected to leads for connection to terminals, wherein a heatresistive. non-electrical conducting coating is applied to the elementto maintain electrical insulation and to bond and maintain the, wire inspatial relation, and wherein a heat resistive non-electrical conductingcoating is applied to the connectionbetween the leads and terminals tobond same together and to maintain electricalintegrity.

Other objects, features and advantages of the invention will be apparentfrom the following detailed disclosure, taken in conjunction with theaccompanying I sheets ,of drawings, wherein like reference numeralsrefer to like parts, in which:

FIG. 1 is a top plan view of one form of the temperature sensitivecontrol sensor used in the cooking unit according to the invention;

FIG. 2 is a front elevational view of the sensor in FIG.

FIG. 3 is an end elevational view of the sensor in FIG.

1 looking at the terminal end;

' FIG.'4 is an'exploded perspective view of the sensor FIG. 8 is a topplan-view of a modified sensor usable I in a cooking unit according tothe invention;

FIG. 9 is an end elevational view of the sensor in FIG. 8, taken fromthe terminal end;

FIG. 10 is a longitudinal sectional view taken substantially along line10-10 of FIG. 8;

FIG. 11 is a top plan view of a further modified sensor usable in acooking unit according to the present invention;

FIG. 12 is an end elevational view of the sensor of FIG. 1 1 taken fromthe terminal end; and

FIG. 13 is a longitudinal sectional view taken sub stantially along line13--l3 of FIG. 1 l.

The cooking unit of the invention includes asensor which is constructedso that it can withstand metal casting processes and be cast directly ina metal mass constituting the cooking unit for cooking food. Forexample, it may be castin aluminum, and therefore, must withstand extremelyhigh temperatures such as about 1,300 F. One form of sensor constructionis illustrated by the sensor 15, which is shown in FIGS. 1 to 4. Thesensor 15 is illustrated in FIG. 6 as it would be cast into a metal mass16 constituting a cooking unit having a cooking surface 17. Thetemperature of the cooking unit 16 would be sensed and controlled by thecontrol sensor 15. As illustrated, the sensor 15 is embedded in thecooking unit 17. It will be appreciated that a heating unit of anydesired type may be arranged with the cooking unit to generate heattherefor.

The sensor-15 includes generally a pair of substantially identicalsheath conductor assemblies 18, a temperature'sensitive resistanceelement 19, a cover 20 over theresistance element 19, and a ceramicinsulant material 21 encapsulating the resistance element 19 within thecover.

The sheath conductor assemblies 18 are arranged in side by siderelationship, and each assembly includes a tubular sheath 22 formed of aductile metal, a terminal or conductor 23 extending through the sheathand protruding from opposite ends, and a ceramic insulant material 24within the sheath and electrically insulating the terminal 23 from thesheath 22. The terminal or conductor 23 is in wire form and of anelectrically conducting metal having a low coefficient of resistancechange with temperature change. For example, a suitable material wouldbe constantan. The ceramic insulant material may be magnesium oxide,aluminum oxide or any other suitable material capable of withstandinghigh temperatures and capable of being effectively used in the processfor forming the sheath conductor assembly. 1

In the construction of a sheath conductor assembly,

the terminal 23 is supported at both ends in relation to the metalsheath 22 at'a center position within the sheath, while the-spacebetween the terminal andthe inside of the sheath is filled with apowdered ceramic insulant material such as magnesium oxide. The sheaththen is swaged or drawn to pack the material tightly within the sheatharound the conductor, and thereby provide a sheath conductor assemblyhaving the conductor or terminal extending therethrough and electricallyinsulated from thesheath. The packed insulant material completely andsealingly fills the area in the sheath between the sheath inner wall andthe conductor, and will take on the character of a solid.

The temperature sensitive resistance element 19, which includes opposedleads 25 is then electrically connected to the adjacent ends ofterminals 23 of side by side sheath conductor assemblies. Connection ismade by welding or brazing the leads to the terminals.

The cover 20 includes a pair of identically formed cover plates 26,which are fabricated to define a U- shaped channel 27. The cover plateswhen brought together on the ends of the sheath conductor assembly 18serve to enclose the temperature sensitive resistance element 19 and theconnections to the terminals 23. Following the connection of thetemperature resistance element 19 to the terminals 23, one of the coverplates 26 is secured to the sheaths 22 of the sheath conductor assembly18 such as by spot welding at the points 28,

FIG. 1. With the cover plate 26 in position, it forms a well orcontainer into which ceramic insulating cement is applied to totallyencapsulate the element 19, its leads and the ends of the terminals 23.Any suitable ceramic insulating cement may be used such as aluminumoxide in a sodium silicate binder. The cement is cured by applying heatand thereafter the other cover plate 26 is arranged in opposed relationto the first cover plate, and suitably spot-welded thereto such as atpoints 29, FIG. 1. It will be appreciated that the ceramic insulatingcement essentially fills the area within the cover between the coverplates and the element 19, the leads 25 and the terminals 23 so thatlittle if any gas space is left which might cause a blowout in thecasting process. Further, the encapsulation of the temperatureresistance element and its leads, and the associate ends of the terminal23 precludes any possible molten metal from seeping in the interior ofthe cover to contact the leads and short out the resistance element. Thecover 20 also provides a support for rigidly holdingthe sheath conductorassemblies together and for holding the re sistance element in properposition relative the sheath assemblies tomaintain integrity andtoespecially protect the resistance element and connections during castingin molten material. Thus, thisembodiment is especially suitable for usein a solid mass. It can be appreciated that the cover plates 26 may bestamped from any ductile formable metal.

The temperature sensitive resistance element 19 is shown in detail inFIG. 5, and includes a cylindrically shaped ceramic core 31 having woundthereon in a helical manner a temperature sensitive resistance wire 32.Each winding is spaced from the next so that the I wire is spatiallywound on the core. The wire is of a type having a high co-efficientresistance change, and may, for example, be iron, analloy of percentnickel and 30 percent iron, or nickel. An end cap and lead as sembly 33is arranged at each end-of the ceramic core 31. Each assembly'includesacup-shaped end cap 34 and alead 35. The lead 35 is the same as thatpreviously identified by the numeral 25 and more generally describedwhen relating'to the assembly sensor shown in FIGS. 1 to 4. The oppositeends of the resistance wire 32 are respectively welded or brazed to theopposing end caps 45 at points 36. The end cap and lead assemblies areof a suitable metal having a low coefficient of resistance change with.temperature change. The.

ceramic core 31 is in rod form and vitrified conditions.

Following the connection of the resistance wire to the end caps, theassembly is coated with a heatrelowing the coating of the assembly, thecoating is cured by applying heat to provide the completed resistanceelement 19. The ceramic cement when in condition is electricallynon-conductive, and serves to bond the end caps to the ceramic coreand'to bond the resistance wire to the core and maintain each winding inspatial and insulated relationship.

tric resistance element also embedded in the mass of the cooking unit,or in the form 'of a fuel burner applying heat to the underside .of'theunit. A constant voltage is applied to the sensor by the controller 39.Sincethe current flow in an electricalcircuit is a functionof circuitresistance, a change in the resistance of the temperature sensitiveresistor 19 of the. sensor will produce a corresponding change incircuit current flow. The controller 39 responds to a current change tocontrol the energy input of the heating unit to the cooking unit,whereby the energy input maybe reduced or increased to counteract theenergy loss or gain and maintain the temperature of the cooking surface17 at a predetermined cooking temperature, such as about 385 F., withinclose limits'to thereby insure consistent high quality and flavorof thefood cooked. v

Another form of temperature sensitive control sensor for use in acooking unit isshown in FIGS. 8 to 10, wherein the sensor generallydesignated by the numeral 15A includes generally an elongated sheath 42,a temperature sensitive I resistance element 19 mounted therein, andterminals or conductors 43 and 44.,The temperature sensitive resistanceelement 19 is identical with that employed in the embodiments of FIGS. 1to 4, but in mounting the resistor within the sheath, the leads 35 aremaintained coaxial with the longitudinal axis of the element rather thanbeing bent normally thereto as in the embodiment of FIGS. 1 to 4. Aceramic insulant material 45 is also arranged within the sheath andelectrically insulates the terminals and resistor 'from the sheath.

The sheath .42 is of a suitable ductile metal such as that used with thesheath 22 of the first embodiment, while the ceramic insulant material45 is of the same type as the material 24 in the first embodiment. Itshould also be appreciated that the terminals 43 and 44 are of the samematerial as the terminals 23 in the first embodiment, wherein they havea low coefficient of resistance change with temperature change.

In order to maintain the integrity of the sensor in its fabrication,inasmuch as a greater portion of the sheath is swaged or drawn to packthe ceramic insulant material about the conductors or terminals, whichswaging effects an elongation of the sheath, the resistor leads 35 areelectrcially connected to the terminals 43 and 44 through springconductors 46. Eachlead 35 ,is welded or brazed to one end of a springconductor, while the other ends of the spring conductors are welded orbrazed to the corresponding ends of the terminals 43 and 44. Thispermits the absorption in change of length in the sheath during swagingwithout rupturing the connections between the resistor leads andterminals.

The fabrication of the sensor 15A includes the interconnection of thesprings and terminals with the resistor leads and the mounting of samein a straight piece .of sheath material. Following the filling of thesheath with a powdered ceramic insulant material, such as magnesiumoxide, the sheath is swaged in the zones 47 and 48, FIG. 8,:therebycompacting the ceramic insulant material and'firmly anchoring thematerials within the sheath. Elongation ,of the sheath in the swagingzones will notcause disconnection of the terminals with respect to theresistor lead because of the spring conductors 46 which are *flexibleNoreduction in diameter is performed in the area of the resistor and itsspring conductors. I-Iowever, the area of the sheath at the resistor I9is crimped in order to maintain the centering of the resistor 19.Accordingly, all stresses between the terminals and resistor leads arerelieved during the swaging operation by the spring conductors 46. Thespring conductors may be in coil form and made .from any ductile metalhaving a low co-efficient of resistance change with temperature change.The assembly after completion of the swaging and crimping operations isthen-formed by conventional tube forming methods, into U shap'e asshown.

Another form. of sensor for use in a cooking unit according to theinvention is shown in FIGS. 11 to 13,

wherein the sensor here, generally indicated by the numeral 15B includesa sheath 50, a terminal or conductor 51 electrically isolated from thesheath by ceramic insulant material 52, and the temperature sensitiveresistor 19.,Construction here is similar to that described relative tothe embodiment in FIGS. 8 to 10, although oneof the leads 35 of theresistor 19 is here electrically connected to the sheath which acts asone of the conductors in the sensor circuit. In this respect, one of theleads 35 is welded at '54 to the sheath 50 at one end thereof. Like theembodiment of FIGS. 8 to 10, a stress relieving spring conductor 55 isconnected to the other resistor lead 35 and in turn to the terminal 51such as by welding or brazing. Following the insertion of the resistorl9, coil spring 55 and terminal 51 within the sheath, the one lead 35 ofthe resistor is welded to the one end of the sheath. Thereafter, poweredmagnesium oxide or the like is introduced within the sheath to fill thearea about the resistor, spring and terminal. The

. ship in respect to the sheath.

A second terminal 57 is then welded to the sheath 50 at the end wherethe terminal 51 protrudes from the sheath for subsequent connection ofthe sensor in the circuit of the controller. The operation of thissensor is the same as the other embodiments, but it will be appreciatedthat this configuration permits grounded sensor circuits where they aredesired. Like the embodiment of FIGS. 8 to 10, this unit is completelysealed by thesheath and the weld at one end, and'therefore it is:

likewise useful in solid, liquid or gas masses.

It will be understood that modifications and variations may be effectedwithout departing from the scope of the novel concepts of the presentinvention, but it is understood that this application is to be limitedonly by the scope of the appended claims.

I claim:

sor comprising metal sheath means, a temperature sensitive resistanceelement having a lead at each end, terminal wire means extending fromthe sheath means and electrically connected to said element, and ceramicinsulant material packed between the terminal wire means and sheathmeans by swaging of said sheath means.

2. The combination as defined in claim 1, wherein said element includesa ceramic core, a temperature sensitive resistance wire wound on saidcore, said wire having a high coefficient of resistance change withtemperature increase, means electrically connecting said leads toopposite ends of said resistance wire and said leads having a lowcoefficient of resistance change with temperature, and an electricallynon-conductive heat resistive coating over the entire element except theends of the leads. v I a 3. The combination as defined in claim 2,wherein the wire is spatially wound on said core.

4.v The combination as defined in claim 1, wherein said sheath meansincludes two side-by-side sheath assemblies including sheaths havingterminals extending therethrough and protruding from opposite ends,ceramic insulant material between the sheaths and terminals and packedby swaging of the sheaths, means electrically connecting the leads ofsaid element to adjacent ends of said terminals at one end of thesheaths, ceramic insulating means encapsulating the element, leads, andterminal ends, and rigid cover plates secured a food cooking surface ofa v said heating means in response to said sensor, said senv over theelement and to the sheaths.

SL The" combination-as definedin claim l, wherein I said terminal wiremeans include a terminal wire connected to each lead of said elementhaving alow coefficient'bf resistance change with temperature.

6I'The combination as defined in claim 5, an

resilient conductors betw eenthe 'element'leads and said terminal wiresto compensate for elongation of the sheath between the adjacent ends ofthe terminals,

minaL, said resistance element being dis osed within e the ermmal andthe s ath ad acent the mner end 0 the adjacent end of the sheath, meansconnecting one lead of the element to the sheath, resilient conductormeans in the form of a coil spring connecting the other lead to theterminal, and said terminal wire means including a second terminalconnected to the exterior of said sheath.

1. The combination of a food cooking surface of a metal cast cooking unit, means for heating the cooking unit to cook food on the surface, a temperature sensitive control sensor cast in the cooking unit during the casting thereof for sensing the temperature of the cooking surface, and a current sensitive controller operating said heating means in response to said sensor, said sensor comprising metal sheath means, a temperature sensitive resistance element having a lead at each end, terminal wire means extending from the sheath means and electrically connected to said element, and ceramic insulant material packed between the terminal wire means and sheath means by swaging of said sheath means.
 2. The combination as defined in claim 1, wherein said element includes a ceramic core, a temperature sensitive resistance wire wound on said core, said wire having a high coefficient of resistance change with temperature increase, means electrically connecting said leads to opposite ends of said resistance wire and said leads having a low coefficient of resistance change with temperature, and an electrically non-conductive heat resistive coating over the entire element except the ends of the leads.
 3. The combination as defined in claim 2, wherein the wire is spatially wound on said core.
 4. The combination as defined in claim 1, wherein said sheath means includes two side-by-side sheath assemblies including sheaths having terminals extending therethrough and protruding from opposite ends, ceramic insulant material between the sheaths and terminals and packed by swaging of the sheaths, means electrically connecting the leads of said element to adjacent ends of said terminals at one end of the sheaths, ceramic insulating means encapsulating the element, leads, and terminal ends, and rigid cover plates secured over the element and to the sheaths.
 5. The combination as defined in claim 1, wherein said terminal wire means include a terminal wire connected to each lead of said element having a low coefficient of resistance change with temperature.
 6. The combination as defined in claim 5, and resilient conductors between the element leads and said terminal wires to compensate for elongation of the sheath means during swaging.
 7. The combination as defined in claim 1, wherein said sheath means includes a single continuous sheath, said terminal wire means including terminals extending from said sheath and inwardly from opposite ends and terminating short of each other, ceramic insulant material packed between the terminals and the sheath by swaging of the sheath in the area of the terminals, said resistance element being disposed within the sheath between the adjacent ends of the terminals, resilient conductor means in the form of coil springs connected between thE terminals and the leads of said elements, and said sheath being U-shaped.
 8. The combination as defined in claim 1, wherein said sheath means includes a straight continuous sheath, said terminal wire means including a single terminal extending from the sheath and inwardly from one end and terminating short of the other end, ceramic insulant material packed between the terminal and sheath by swaging of the sheath in the area of the terminal, said resistance element being disposed within the sheath adjacent the inner end of the terminal and the adjacent end of the sheath, means connecting one lead of the element to the sheath, resilient conductor means in the form of a coil spring connecting the other lead to the terminal, and said terminal wire means including a second terminal connected to the exterior of said sheath. 